1. Field of the Invention
This invention relates to an improved method for the production of 2-mercaptobenzothiazole.
More particularly, the invention relates to an improvement in a method for the production of 2-mercaptobenzothiazole from aniline, nitrobenzene, and carbon disulfide.
2. Description of Related Art
It is well known that 2-mercaptobenzothiazole is useful as a vulcanization accelerator for natural and synthetic rubbers and as a starting material in the synthesis of other thiazole compounds that are also useful as vulcanization accelerators.
One commercial means for the synthesis of 2-mercaptobenzothiazole involves the reaction of aniline, carbon disulfide, and sulfur. The overall chemistry of this reaction can be represented by the following equation. ##STR1##
Although this chemistry is straightforward, it is an oversimplification of the actual chemistry, which occurs through a variety of intermediates.
U.S. Pat. No. 1,712,968 discloses a process wherein an aromatic thiourea, e.g., thiocarbanilide, is reacted with carbon disulfide and sulfur according to the equation: ##STR2##
The reaction is run in an autoclave, which is slowly heated so that the temperature of the contents of the autoclave increases at a rate of approximately one degree per minute. This rate of heating is continued until the temperature reaches 225.degree. C., whereupon the heat is moderated so that the temperature rise is about one degree every two minutes, and this rate is continued until the contents of the autoclave has reached a temperature of about 275.degree. C. The time required for attaining the temperature mentioned under the conditions specified is approximately from five to six hours.
U.S. Pat. No. 2,001,587 discloses a method for preparing mercapto arylene thiazoles consisting of reacting a mixture of carbon disulfide, and arylamine and an organic oxidizing agent, such as an aromatic nitro compound, according to the equation: ##STR3##
wherein R represents an aromatic nucleus. The reactants are heated in an autoclave at 220.degree. C. for six hours.
U.S. Pat. No. 3,818,025 discloses a process for the production of 2-mercaptobenzothiazole by the reaction of aniline, carbon disulfide and sulfur at a high temperature under elevated pressure, characterized in that the reaction is carried out first at 250.degree. to 300.degree. C. and then at 200.degree. to 240.degree. C.
U.S. Pat. No. 4,316,031 discloses a process for the preparation of 2-mercaptobenzothiazole comprising heating a reaction mixture comprising nitrosobenzene, hydrogen sulfide and carbon disulfide in a molar ratio of about 1: 1.5 to 4:1 to 3, respectively, to a temperature from about 200 to about 300.degree. C., for a time sufficient to convert at least a portion of the reactants into 2-mercaptobenzothiazole. In an alternative process, there is first reacted nitrosobenzene with hydrogen sulfide in a molar ratio of about 1:1.5 to 4, at a temperature from about 20 to about 100.degree. C. for a period of time sufficient to substantially reduce the nitrosobenzene, and subsequently reacting the resulting product mixture with from about 1 to about 3 mole equivalents of carbon disulfide per mole of originally charged nitrosobenzene, at a temperature from about 200.degree. C. to about 300.degree. C.
U.K. Patent Application GB 2 018 774 A discloses a process for the preparation of 2-mercaptobenzothiazole which comprises reacting nitrobenzene or nitrosobenzene, hydrogen sulphide and carbon disulphide, the molar ratio of nitrobenzene or nitrosobenzene:hydrogen sulphide being from 1:3 to 1:6 or from 1:1.5 to 1:4, the molar ratio of nitrobenzene or nitrosobenzene:carbon disulphide being from 1:1 to 1:3 and the final reaction temperature being from 200 to 300.degree. C.
Embodiments are disclosed wherein (a) nitrobenzene and H.sub.2 S are reacted in a specified molar ratio under elevated temperature and pressure and the resulting reaction mixture is reacted with CS.sub.2 in a specified molar ratio at 200 to 300.degree. C.; (b) nitrosobenzene, H.sub.2 S and CS.sub.2 are reacted in a specified molar ratio at 200 to 300.degree. C.; and (c) nitrosobenzene and H.sub.2 S are reacted in a specified molar ratio at 20 to 100.degree. C. and the resulting reaction mixture is reacted with CS.sub.2 in a specified molar ratio at 200 to 300.degree. C.
The disclosures of the foregoing are incorporated herein by reference in their entirety.